Questions - Answers
4 Marks Questions:
1. Explain homogeneous and heterogeneous catalysis.
A: Homogeneous Catalysis: The catalysis in which the reactants and catalyst are in the same phase (gas or liquid)
e.g.: 2 SO2 (g) + O2 (g) 
2 SO3
Heterogeneous Catalysis: The catalysis in which the reactants and catalyst are in different phases.
e.g.: N2 (g) + 3 H2 (g) 
2 NH3
2. Give 4 characteristics of Catalyst?
A: A catalyst does not initiate the reaction. It doesn't effect the position of the equilibrium. It is not consumed during the reaction. Acatalyst may increase or decrease the rate of a reaction. Change of temperature can change the rate of catalytic reaction. It's action is more in powdered state. A small amount of catalyst is enough to carry the reaction. The catalyst is specific in nature.
3. Explain Tyndall effect and Brownian movement.
A: "The phenomenon of scattering of light by colloidal particles in all directions and formation of bright glowing cones is known as Tyndal effect"
The continuous rapid zig - zag movement by colloidal particles in the dispersion
medium is known as Brownian movement.
4. Write any four differences between physical adsorption and chemical adsorption?
A:
5. Give any 4 differences between true solution and colloidal solution?
A:
6. Write any four differences between lyophilic colloids and lyophobic colloids?
A:
7. What is micelle? Explain the cleaning action of Soap.
A: "Micelle is the colloidal sized particle which is formed when small molecules or ions associate together. Micelle has hydrophilic end (head) and hydrophobic end (tail)".
Stearate micelle
Cleansing action of Soap: Soap is considered as Sodium Stearate. It has C17H35 COO- (Stearate) and Na+ ions. Stearate ion has C17H35 non polar part (tail) which attracts and dissolves grease, where as COO- is polar part (head) which attracts water. In concentrated solution of soap, micelles are formed. The grease part of cloth is dissolved by tail part and head part attracts water to form emulsion. Thus soap helps in emulsification and washing away of oils and fats (dirt form).
8. What is Coagulation? Write about Hardy-Schulze law.
A: Coagulation is taking place when the colloidal particles lose the charge and coming down as precipitate when electrolyte is added to it. This law states that "The coagulating ability of oppositely charged ions is directly proportional to the charge of coagulating ions''.
Coagulating ability of positive colloid: Cl-< SO4-2< PO4-3
Coagulating ability of negative colloid: K+< Ba+2< Al+3
9. Identify dispersed phase and dispersion medium present in a) Smoke b) Cloud c) Blood d) Milk.
A:
10. What are enzymes? Name any 2 enzyme catalysed reactions.
A: Proteins with high molecular mass, which forms colloidal solution in water are called enzymes.
e.g.: 1) Inversion of cane sugar.
2) Conversion of glucose into ethyl alcohol:
11. Explain the following terms
a) Peptization b) Dialysis c) Electrophoresis d) Zeta Potential
A: a) Peptization: The conversion of precipitate into colloidal sol by shaking it in presence of electrolyte present in dispersion medium.
b) Dialysis: The process of removal of dissolved impurities present in colloidal solution by using dialysing membrane.
c) Electrophoresis: Migration of colloidal particles under applied emf.
d) Zeta potential: The potential difference between the fixed layer and the diffused layer (of opposite charge).
12. Explain the following terms
a) Sol b) gel c) foam d) aerosol
A: a) Sol: The colloidal system in which dispersed phase is solid & dispersion medium is liquid. e.g.: paint.
b) Gel: The colloidal system in which dispersed phase is liquid & dispersion medium is solid. e.g.: Jelly.
c) foam: The colloidal system in which dispersed phase is gas & dispersion medium is liquid. e.g.: Soap lather.
d) Aerosol: The colloidal system in which dispersed phase is liquid & dispersion medium is gas. e.g.: Cloud.
13. Explain the following terms
a) Adsorption b) Absorption c) Sorption d) Desorption
A: a) Adsorption: The process of accumulation of adsorbate molecules on the surface of adsorbent (solid or liquid).
b) Absorption: The process in which molecules remain not only at the surface but also go deep into bulk.
c) Sorption: The simultaneous process of adsorption along with absorption.
d) desorption: The removal of adsorbate molecules from the surface of adsorbent.
14. Describe Bredig's arc method of preparation of colloids with a neat diagram.
A: Gold, Silver and Platinum colloids are prepared by this method. It involves dispersion and condensation. Electric arc is given between 2 metal electrodes placed in dispersion medium. Colloidal solution is formed due to heat produced in arc.
2 Marks Questions:
1. Define "Gold Number".
A: The minimum number of milligrams of lyophilic colloid required to prevent the coagulation of a standard gold sol on addition of 1ml of 10% NaCl solution.
2. Give the signs of ΔH & ΔS, when ammonia gas gets adsorbed on Charcoal.
A: ΔH = -Ve, ΔS = -Ve as adsorpton of NH3 on charcoal is exothermic reaction.
3. Define "promoter" and "poison" in the phenamenon of Catalysis.
A: Promoter: The substance that enhance the activity of a catalyst.
Poison: The substance that decrease the activity of a catalyst.
4. What is Critical Micelle Concentration (CMC) and Kraft temperature (Tk)?
A: CMC: The concentration at which micelles are formed.
Tk: The temperature at which micelles are formed.
5. Give any 2 applications of adsorption.
A: → In froth flotation process.
→ In the separation of mixture of noble gases on coconut charcoal.
6. Why Zeolites are treated as shape selective catalysts? Which Zeolite catalyst is used to convert alcohols directly into gasoline?
A: Zeolites have honey comb like structure.
ZSM-5 converts alcohol directly into gasoline (Petrol).
7. Give 2 applications of colloids.
A: → In the purification of drinking water by alum.
→ In the cleansing action of soaps and detergents.
